This invention relates to a hydraulic control valve apparatus and particularly to a drive mechanism for a valve of a hydraulic control valve apparatus.
A typical hydraulic control valve apparatus in which the switching of the fluid is achieved by an electrical signal is arranged, as shown in FIG. 1, such that the electrical signal is applied to a coil C of an electromagnetic solenoid ES comprising a plunger P, the coil C, a yoke Y and a return spring RS to obtain a displacement which is utilized to operate a valve V, thereby achieving the switching of the hydraulic fluid.
In the hydraulic control valve apparatus employing an electromagnetic solenoid as a drive unit, the electromagnetic solenoid has a clearance or gap of distance L between one end of the plunger P and one end of the yoke Y. The gap distance L is normally maintained by the return spring RS. When the coil C is excited by an electrical signal, the plunger P is magnetically driven to apply its force F to the valve V, thereby to achieve the valve operation. Since the driving force F of the electromagnetic solenoid ES decreases in inverse proportion to the second power of the gap distance L, the initial driving force for of the electromagnetic solenoid must be larger than the operating load f1 of the valve V. Therefore, at the time of stopping of the actuation of the plunger, a heavy impact due to an excessive force f2 shown in the FIG. 2 is experienced, resulting in decrease in the durability of the electromagnetic solenoid which disadvantageously decreases operational reliability.
Also, since the drive force F is inversely proportional to the second power of the gap distance L as seen from the characteristic curve shown in FIG. 2, when the operating stroke and required drive power of the valve are great, it has been necessary either to make the electromagnetic solenoid larger or to provide a levering mechanism or the like for increasing the plunger displacement. This has been disadvantageous in that the structure of the hydraulic control valve apparatus becomes complicated and response is degraded.
Puffer-type circuit interrupters have been widely used in which an SF.sub.6 gas having good electrically insulating and current interrupting capabilities is used as an arc extinguishing medium whereby the high pressure SF.sub.6 gas compressed within a puffer chamber is blasted into an electric arc to extinguish.
Most of the operating mechanism for use in puffer-type circuit interrupters of 300 KV or 500 KV class are of the hydraulic operating type, which can realize high speed interruption within 2 cycles because of the large operating force available, improving the interrupting capability.
The hydraulic operating system uses a fluid at a higher pressure than that in a compressed air operating system, so that the operating mechanism can be made compact and inexpensive. However, as the circuit interrupter becomes higher in operating speed, the hydraulic operating mechanisms and the control units therefor such as the electromagnetic switching valve inevitably also become large. Electromagnetic switching valves generally used are electromagnetic repulsive control valves, which naturally must be made large if a great force is to be provided.
Recently, as circuit interrupters come to have higher speeds and improved interrupting capability, free speed control and stopping with reduced shock to the drive unit are being considered more important. For example, as apparent from the travel curve (stroke-time curve) of a circuit interrupter shown in FIG. 7, the travel curve without speed control (shown by a broken line) during the operation of the puffer-type circuit interrupter is distorted and disadvantageously affects the interrupting capability of the interrupter.
In the conventional systems in which the previously mentioned electromagnetic repulsive control valve is used, the stop position of the drive unit cannot be controlled, so that the speed of the drive unit must be controlled by configuring the diameter of the contraction valve to a predetermined dimension. Therefore, changing the speed pattern during the design of the interrupter and the operating mechanism is difficult, posing a difficult problem to be solved.
Also, in order to solve the problems involved in a high speed circuit interrupter and to answer the demand for improved interrupting performance, a suitable interrupting speed must be selected in accordance with the voltage and the current conditions of the lines to be protected at the time of interruption, and in order to improve the reliability of the circuit interrupter, the massive stress often exerted on the drive of the circuit interrupter should be reduced. Further, the range of interruption conditions which can be covered by the circuit interrupter can be increased by selecting an interrupting speed with the parameters determining the interrupting duty, such as the current to be interrupted, taken into consideration and by changing the speed pattern during the interrupting operation, whereby the interrupting capability of the circuit interrupter is improved. It is therefore desirable to provide an arrangement in which the speed control of the circuit interrupter can be achieved on an on-line basis.